uniform sampler2D sampler;
uniform float opacity;
uniform float brightness;
uniform float saturation;

varying vec2 varyingTexCoords;

void main()
{
    vec4 tex = texture2D(sampler, varyingTexCoords);
    if( saturation != 1.0 )
        {
        vec3 desaturated = tex.rgb * vec3( 0.30, 0.59, 0.11 );
        desaturated = vec3( dot( desaturated, tex.rgb ));
        tex.rgb = tex.rgb * vec3( saturation ) + desaturated * vec3( 1.0 - saturation );
        }
//     tex.rgb = tex.rgb * opacity * brightness;
//     tex.a = tex.a * opacity;
    gl_FragColor = tex;
}
